This invention relates generally to closure devices for large diameter tubes. More particularly, the present invention relates to closure devices for fuel transfer tubes at nuclear power plants.
Nuclear power plant fuel must be kept under water when it is transferred to and from the reactor core to minimize radiation exposure to personnel and equipment. Fuel is transferred to and from the reactor containment via a fuel transfer tube. The fuel transfer tubes are generally designed and constructed to utilize a blind flange closure on the containment side of the tube when the tube is not actively being used. Such blind flange closures utilize a plurality of studs and nuts to mount the closure device to the tube. Installation of the closure device requires that the blind flange be positioned and properly aligned with the studs. Nuts must be threaded on each stud and torqued to a predetermined value. This process is reversed during removal of the closure device. These procedures are time consuming, resulting in high operating costs and high personnel radiation exposure.
In addition, the studs and nuts are subject to cross-threading and galling when the nuts are being installed or removed from the studs. Damaged studs must be replaced to provide a proper seal for the closure device, resulting in additional operating costs and personnel radiation exposure.